diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -2476,6 +2476,14 @@
   if (Next->MatchingParen->Next &&
       Next->MatchingParen->Next->is(TT_PointerOrReference))
     return true;
+  // Check for K&R C function definitions, e.g.:
+  //   int f(i)
+  //   {
+  //     return i + 1;
+  //   }
+  if (Next->Next && Next->Next->is(tok::identifier) &&
+      !(Next->MatchingParen->Next && Next->MatchingParen->Next->is(tok::semi)))
+    return true;
   for (const FormatToken *Tok = Next->Next; Tok && Tok != Next->MatchingParen;
        Tok = Tok->Next) {
     if (Tok->is(TT_TypeDeclarationParen))
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -8209,6 +8209,16 @@
                "}\n",
                Style);
 
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterFunction = true;
+  verifyFormat("int f(i);\n" // No break here.
+               "int\n"       // Break here.
+               "f(i)\n"
+               "{\n"
+               "  return i + 1;\n"
+               "}\n",
+               Style);
+
   Style = getGNUStyle();
 
   // Test for comments at the end of function declarations.